We shall carry out a detailed analysis of membrane transport mechanisms in several animal parasites, with a view to developing a concept of the degree of variability in such systems among animal parasites. This will include study of interactions of metabolites transported. An analysis will be made of energy flow and exchange of certain metabolites between selected hosts and parasites. Experimental study of the interactions of extrinsic host enzymes with the surfaces of intact parasites will be performed, with special attention to the relation of such interactions to the flow of metabolites into parasites. Similarly, intrinsic membrane-bound enzymes of parasite surfaces will be sought and will be characterized.